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Research at the SLOWPOKE-2 Facility

The SLOWPOKE-2 at RMC provides an intense neutron source used for teaching, training and research. It is currently used by researchers at RMC, Queen’s University, and the Department of National Defence. Some of the analytical applications that are made possible by the reactor include neutron activation analysis, neutron radiography, delayed neutron analysis, production of small amounts of short-lived radioisotopes and radiation processing.

Neutron Activation Analysis

The very stable thermal neutron flux produced by SLOWPOKE-2 is ideal for an analytical technique known as neutron activation. Neutron activation analysis is a sensitive tool that provides the ability to determine the elemental composition of materials. Gamm

NAA has advantages over other experimental techniques for it requires only a small amount of sample material, has very little sample preparation involved, and is able to perform multi-element identification efficiently while having extremely sensitive detection limits.

In NAA, a neutron is absorbed by a nucleus in the target material. This results in the formation of a compound nucleus which, when radioactive, decays, typically by beta emission, to a daughter nucleus. The daughter nucleus is generally left in an excited state and relaxes through the emission of characteristic gamma rays.

If a sample is composed of several different nuclei, multiple excited daughter products are produced. This leads to an energy spectrum of characteristic gamma rays. The energy spectrum is analyzed using a high purity germanium crystal detector coupled to a spectrometer which determines the elemental composition of the sample. This makes NAA a very powerful method for elemental and isotopic studies of unknown samples. RMC employs neutron activation techniques for many projects including the analysis of trace elements for quality control in plastics, analysis of various research materials for very low trace concentrations of contaminants, gamma ray spectroscopy on water, seawater, soils, biota and cement dust, cleanup by first responders during exercises, and for teaching of undergraduate and graduate students.

Neutron Radiography

Neutron radiography is another non-destructive technique utilizing the neutron flow produced by the SLOWPOKE-2 reactor. This method allows for the discrimination of materials of similar density and provides a picture of the internal structure of the object.

Neutron radiography functions on the basis of transmission of neutrons through material samples. A neutron beam is directed onto an object of interest and, because neutron interactions with materials vary with composition and density of the target, an image of the internal structure of the object is produced. Neutrons have a large penetration depth into most materials, and their behaviour is particularly affected in low mass materials. Neutron radiography is successfully used to study the internal structure of CF-188 flight surfaces, detecting abnormalities in the internal structure such as moisture ingression, structural corrosion, and physical damage.

The internal structure of a CF-18 flight surface is comprised of a honeycomb composite. Under operating conditions, a CF-18 wing undergoes severe stresses. These stresses cause damage which is both difficult to detect and costly to fix if left unattended. Moreover, structural damage may result in catastrophic situations during flight. Routine neutron radiography allows the maintenance of these flight surfaces through identification of problem sites while they are still manageable thus reducing cost and increasing reliability and safety of equipment.

Water ingress in a CF-18 rudder (Image courtesy of Major Paul Hungler)

Delayed Neutron Counting System

A Delayed Neutron Counting System has recently been built in the SLOWPOKE-2 Facility and is currently being validated. This system detects the delayed neutrons that are released from some of the fission products thereby giving the RMC the ability to detect uranium and plutonium in special nuclear materials. The DNCS takes advantage of the already present capabilities offered by the SLOWPOKE-2 Facility and further expands the analytical tools available to its users.

Radiation Processing

Thanks to its open pool concept, the SLOWPOKE-2 nuclear reactor allows the research staff and students to carry out radiation processing of materials. At the RMC, the research has focussed on polymers, polymer-based adhesives and polymer-based composite materials. The effects of the mixed radiation field produced by the SLOWPOKE-2 nuclear reactor are summarized in a phenomenon called cross-linking in which the materials become stronger, and in a competing effect called chain scission in which the long molecular chains are broken into shorter segments, making the material weaker and easier to break. The reactor was used in an investigation of polymer-based adhesives for applications in the construction of space vehicles. The research has resulted in a significant improvement of the adhesive properties of several materials from the interaction of ionizing radiation imparted to samples positioned in the reactor pool close to the reactor core.

Most of the research carried out at RMC in this domain has investigated polymer-based composites as potential materials for the fabrication of leak-tight containers intended at isolating the spent CANDU nuclear fuel and other radioactive waste from the biosphere for periods up to 500 years and more in a harsh environment representing the conditions of disposal of the radioactive materials deep underground in the Canadian Shield. The NSERC-funded research has permitted to identify several candidate composite materials such as PolyEtherEtherKetone (PEEK) and PolyEtherImide (PEI) that compare favourably with metals and alloys both in mechanical strength and in resistance to radiation and corrosion.